Selective Isomerization of n-Butane over Mordenite Nanoparticles Fabricated by a Sequential Ball Milling-Recrystallization-Dealumination Route

For the first time, a sequential fabrication step involving mechanochemistry, recrystallization, and dealumination was developed to convert low-cost natural zeolites to mordenite (MOR) nanoparticles. Natural zeolites are mostly found having poor textural properties and a high aluminum content, which are not suitable for most industrial catalytic reactions. The parent natural zeolites within the size of 1-10 μm were treated by ball milling to obtain nanosized particles with size in the range of 20-160 nm. The nitrogen physisorption study revealed that the external surface area and intercrystalline mesopore volume of the milled nanoparticles increased by 4- and 7-fold, respectively. Recrystallization by hydrothermal treatment in basic silicate solution was applied to recover the MOR crystallinity at 170 °C for 6 h. The recrystallized MOR samples were further subjected to acid dealumination treatment over different periods. The H-MOR samples were evaluated in a fixed-bed reactor for n-butane isomerization. The isobutane selectivity increased from 11 to 28% when the parent microparticle was substituted by the recrystallized nanoparticles. Moreover, the catalyst stability improved over the recrystallized nanoparticles. The dealuminated-recrystallized nanoparticle exhibited the highest selectivity of ca. 58% to isobutane and less deactivation rate as a result of low acid site density and small nanoparticle size.